Our working paradigm is that there is a genetic basis to human disease and that understanding the genetic basis of disease will foster development of better diagnostic and treatment strategies. We study Mendelian diseases to identify the underlying gene defect and to understand how the product(s) of this/these gene mutation(s) result in abnormal development or disease. In some cases we have developed animal models (transgenic mice) and in vitro cell models to study disease pathogeneses. Progress during the last year is reported below. Mutant DLX 3 disrupts odontoblast polarization and dentin formation Tricho-dento-osseous (TDO) syndrome is an autosomal dominant disorder characterized by abnormalities in the thickness and density of bones and teeth. A 4-bp deletion mutation in the Distal-Less 3 (DLX3) gene is etiologic for most cases of TDO. To investigate the in vivo role of mutant DLX3 (MT-DLX3) on dentin development, we generated transgenic (TG) mice expressing MT-DLX3 driven by a mouse 2.3 Col1A1 promoter. Dentin defects were radiographically evident in all teeth and the size of the nonmineralized pulp was enlarged in TG mice, consistent with clinical characteristics in patients with TDO. High-resolution radiography, microcomputed tomography, and SEM revealed a reduced zone of mineralized dentin with anomalies in the number and organization of dentinal tubules in MT-DLX3 TG mice. Histological and immunohistochemical studies demonstrated that the decreased dentin was accompanied by altered odontoblast cytology that included disruption of odontoblast polarization and reduced numbers of odontoblasts. TUNEL assays indicated enhanced odontoblast apoptosis. Expression levels of the apoptotic marker, caspase-3, were increased in odontoblasts in TG mice as well as in odontoblastic-like MDPC-23 cells transfected with MT-DLX3 cDNA. Expression of Runx2, Wnt 10A, and TBC1D19 colocalized with DLX3 expression in odontoblasts, and MT-DLX3 significantly reduced expression of all three genes. TBC1D19 functions in cell polarity and decreased TBC1D19 expression may contribute to the observed disruption of odontoblast polarity and apoptosis. These data indicate that MT-DLX3 acts to disrupt odontoblast cytodifferentiation leading to odontoblast apoptosis, and aberrations of dentin tubule formation and dentin matrix production, resulting in decreased dentin and taurodontism. In summary, this TG model demonstrates that MT-DLX3 has differential effects on matrix production and mineralization in dentin and bone and provides a novel tool for the investigation of odontoblast biology. Craniofacial and dental findings in cystinosis Cystinosis is a rare autosomal recessive lysosomal storage disorder with developmental and mineralization anomalies as part of its clinical presentation. The objective of this study was to provide the first systematic assessment of the craniofacial and dental characteristics associated with cystinosis. Oral and radiographic evaluations were performed on 73 patients with cystinosis. Analyses of cephalometry (n = 20), taurodontism (n = 47), caries (n = 47), enamel defects (n = 48), soft tissue anomalies (n = 48), and dental age (n = 41) were performed on the cystinosis group, and compared with age- and sex-comparable controls or standards. Cystinosis patients manifested relative mandibular deficiency, an increased facial height, and a reduced airway space. Taurodontism and enamel defects were significantly more prevalent in cystinosis patients compared with controls (P <0.0001 and P = 0.027, respectively). Children (aged <15 years) with cystinosis also demonstrated a significant delay, of almost 9 months, of their dental development (P <0.001). Novel craniofacial and dental features are associated with cystinosis. Craniofacial deficiencies may influence the swallowing and respiratory complications seen in cystinosis. Renal pathology and associated mineral imbalance may explain the dental root and enamel anomalies found in cystinosis patients;the developmental delays in cystinosis include delayed dental formation. Novel cathepsin C mutation in a Brazilian family with Papillon-Lefvre syndrome: case report and mutation update Papilion-Lefevre syndrome (PLS) is a rare autosomal recessive disorder that involves palmoplantar keratosis (PK) and severe aggressive periodontitis. Cathepsin C (CTSC) gene mutations are etiologic for PLS, with more than 60 different mutations reported in different ethnic groups worldwide. The purpose of this study was to report a novel cathepsin C mutation in a Brazilian patient. A 4-year-old boy presented with aggressive periodontitis, recession, missing teeth, and hyperkeratosis of the palms of hands and soles. Peripheral blood samples were obtained from family members for genomic DNA isolation. The coding region and exon/intron boundaries of the CTSC gene were amplified and sequenced. The patient had a PLS phenotype, which included PK and early-onset severe periodontitis. Sequence analysis showed a novel CTSC mutation (c.267-268del) present in the homozygous state. This report described a novel mutation in a family with Brazilian Papillon-Lefvre syndrome and presented a review of all cathepsin C (65) mutations reported to date. Oral rehabilitation of a patient with amelogenesis imperfecta. Amelogenesis imperfecta is a hereditary disorder that causes defective enamel development in the primary and permanent teeth. Clinical treatment is important to address the esthetic appearance of affected teeth, reduce dentinal sensitivity, preserve tooth structure, and optimize masticatory function. The purpose of this case report was to describe the diagnosis, treatment planning, and dental rehabilitation of a patient with autosomal recessive amelogenesis imperfecta. The patient was followed for 5 years, and evaluation 3 years after restorations revealed no pathology associated with the rehabilitation. The patient's esthetic and functional expectations were satisfied.